I have tried ATLauncher, several modpacks and all. Here is the difference between ATLauncher and FTB. FTB takes time, goes through tremendous amount of work not only to look good and simple at launcher but also make all the mods in mod packs get along with each other BEFORE sending it out. ATLauncher like many game developers out there, the slap together the mods into mod packs, few hasty fixes in config and ID and blam they sent it out. I have tried one of the mod pack, almost daily basis there were new patches and fixes that some old world became dangerous to use.
ATLauncher also restrict on certain thing such as certain mods cannot be removed while few are optional. Where as in FTB, almost everything can be removed, updated or added without restriction. Ultimatly, I deleted ATLauncher and just going to wait for FTB 1.6.x
Yes I am one of those who is impatient and want the DW20 1.6 now, but after 16 years of beta testing games for many companies along with several years 3rd Party QA for SOE, trust me, the wait is well worth it. Yes it is true that the more people play with modpack tend to find bugs and glitches faster than just a dozen modders, but lets be honest...how many players out there really going to report a bug in full details without raging, whining, complaining, cursing, etc? Might as well make the players wait a little longer for FTB get "quality" product out than opening the "whining - its borked" flood gate on forums.
I personally wished I knew how to program anything, even a freaking mining turtle, let alone javascript. But I also see from their point of view (the modders and FTB team) its a freaking nightmare. My full respect for them and thanks for their hard work during "free" time they have. While we wait for new FTB launcher/mod packs... lets entertain ourselves with other games, or maybe good time to learn how to setup your own modpack and coding
PS: I avoid Tekkit after the last fallout a while back.